1. Field of the Invention
The present invention relates to a silicon optoelectronic device and an image input/output device using the silicon optoelectronic device, and more particularly, to a silicon optoelectronic device capable of both emitting and detecting light and an image input/output device using the silicon optoelectronic device to input/output a picture signal on a pixel-by-pixel basis.
2. Description of the Related Art
Most integrated circuits use silicon (Si) as their base material. Si substrates ensure excellent reliability and high integration density when integrating logic elements, operational elements, and drive elements within the substrate. Further, since Si is low in price, Si can be used to realize highly integrated circuits more cheaply than compound semiconductors.
However, Si has an indirect transition energy band gap that makes light emission therefrom difficult. Therefore, light-emitting devices, such as a light emitting diode (LED), are usually fabricated using compound semiconductor materials that have a direct transition band gap and provide excellent light-emitting properties.
These light-emitting devices emit light only when a current exceeding a predetermined threshold is applied. Thus, in order to supply current at an appropriate level, each light-emitting device requires an amplifying circuit and/or a switching circuit. The amplifying circuit amplifies a small amount of current to a level that causes a light-emitting device to oscillate. The switching circuit controls on/off operation for light emission.
The resultant hybrid junctions make it impractical to integrally fabricate the light-emitting devices made of compound semiconductor materials with amplifying circuits and/or switching circuits made of Si in a semiconductor fabrication process. Thus, it is necessary to install amplifying circuits and/or switching circuits fabricated in a process separate from that for making the light-emitting device. However, providing such separately fabricated amplifying circuits makes high speed switching difficult, due to reactance and capacitance parasitic effects arising from the external power lines.
When using an array of light-emitting elements made of compound semiconductor materials as a display device, for example, switching circuits need to be provided outside each of the light-emitting elements so that light emission can occur on a pixel-by-pixel basis. However, such external provision makes it difficult to control the turn-on and turn-off time of current used for light emission on a pixel-by-pixel basis, which hinders control of the duration of light emission.
There is also an increasing demand for taking and transmitting photographs to others and/or displaying a photograph sent from others, especially over the Internet and mobile phones. To meet this increasing demand, as shown in FIG. 1, a separate camera 2 has been installed in a computer system in addition to a monitor 1 for displaying an image. This allows an operator to view, send and transmit photographs. In FIG. 1, the computer system also includes a central processing unit (CPU) 3 and a keyboard 4 or other interactive device. Since a conventional display device such as a typical computer monitor 1 can simply display images, a separate camera 2 is required to photograph an object desired by an operator in order to make visual communications with the other party.
In order to photograph oneself while being able to see the display device, the operator has to position a camera away from the display device. Thus, it is impossible to photograph the operator right in front of the image viewed on the display device, which reduces the vividness in interactive visual communications.